Dual control of vascular tone and remodelling by ATP released from nerves and endothelial cells

Purinergic signalling is important both in short-term control of vascular tone and in longer-term control of cell proliferation, migration and death involved in vascular remodelling. There is dual control of vascular tone by ATP released from perivascular nerves and by ATP released from endothelial cells in response to changes in blood flow (shear stress) and hypoxia. Both ATP and its breakdown product, adenosine, regulate smooth muscle and endothelial cell proliferation. The involvement of these regulatory mechanisms in pathological conditions, including hypertension, atherosclerosis, restenosis, diabetes and vascular pain, are discussed

Arteriogenesis versus angiogenesis: similarities and differences

Cardiovascular diseases account for more than half of total mortality before the age of 75 in industrialized countries. To develop therapies promoting the compensatory growth of blood vessels could be superior to palliative surgical surgical interventions. Therefore, much effort has been put into investigating underlying mechanisms. Depending on the initial trigger, growth of blood vessels in adult organisms proceeds via two major processes, angiogenesis and arteriogenesis. While angiogenesis is induced by hypoxia and results in new capillaries, arteriogenesis is induced by physical forces, most importantly fluid shear stress. Consequently, chronically elevated fluid shear stress was found to be the strongest trigger under experimental conditions. Arteriogenesis describes the remodelling of pre-existing arterio-arteriolar anastomoses to completely developed and functional arteries. In both growth processes, enlargement of vascular wall structures was proposed to be covered by proliferation of existing wall cells. Recently, increasing evidence emerges, implicating a pivotal role for circulating cells, above all blood monocytes, in vascular growth processes. Since it has been shown that monocytes/macrophage release a cocktail of chemokines, growth factors and proteases involved in vascular growth, their contribution seems to be of a paracrine fashion. A similar role is currently discussed for various populations of bone-marrow derived stem cells and endothelial progenitors. In contrast, the initial hypothesis that these cells -after undergoing a (trans-)differentiation- contribute by a structural integration into the growing vessel wall, is increasingly challenged

Role of shear stress in angiopoietin-2-dependent neovascularization: implications in occlusive vascular disease and atherosclerosis

Neovascularization, or the formation of blood vessels, is important in both normal physiological processes as well as pathophysiological processes. The main players in neovascularization, endothelial cells (EC), are highly influenced by hemodynamic shear stress and this may play an important role in neovascularization. Two typical types of shear stress found in the vascular system are a unidirectional laminar shear stress (LS) found in straight regions and a disturbed, oscillatory shear stress (OS) found at branches or curves. At the cellular level, LS is thought to promote EC quiescence whereas OS is thought to promote EC dysfunction. Oscillatory sheared EC are pro-proliferative, pro-migratory, and secrete growth factors, all functions important in neovascularization. There are several diseases that involve both disturbed shear stress and neovascularization, such as atherosclerosis, aortic valve disease, and occlusive vascular disease. In these pathophysiological scenarios fluid shear stress may provide a driving force for neovascularization. Therefore, we hypothesized that oscillatory shear stress promotes greater neovascularization compared to unidirectional laminar shear stress through the secretion of angiogenic factors, which play a physiological role in neovascularization in vivo. To test this hypothesis, we first performed tubule formation and migration assays, two important functions in neovessel formation. We found that OS promotes greater tubule formation and migration of EC as compared to LS and this was mediated through secreted factors. Using gene and protein array analysis, we identified Angiopoietin-2 (Ang2) as being upregulated by OS compared to LS in EC. We found that inhibiting Ang2 blocked OS-mediated tubule formation and migration and that LS-inhibited tubule formation could be rescued by addition of Ang2. In addition, Ang2 was found to be upregulated at sites of disturbed flow in vivo, implicating a physiological role for Ang2. To further investigate the physiological role of Ang2 in neovascularization, we examined the effects of inhibiting Ang2 in a mouse model of hindlimb ischemia, which involves both disturbed flow and neovascularization. We found that Ang2 was upregulated in the ischemic adductor muscle suggesting that it plays a role in recovery during hindlimb ischemia. In addition, we found that inhibiting Ang2 decreased blood flow recovery. Ang2 inhibition resulted in decreased smooth muscle cell coverage of vessels as well as decreased macrophage infiltration. These findings suggest that Ang2 promotes blood flow recovery through the recruitment of smooth muscle cells and formation of collaterals, as well as the recruitment of macrophages that secrete important growth factors and help degrade the extracellular matrix in order for neovascularization to occur. In conclusion, this work illustrates the shear stress regulation of neovessel formation through the expression of Ang2, and the role of Ang2 in neovascularization in vivo. By understanding how angiogenic factors are regulated and what role they play in vivo, we can better understand human disease and develop important therapeutic targets.Ph.D.Committee Chair: Jo, Hanjoong; Committee Member: McIntire, Larry; Committee Member: Nie, Shuming; Committee Member: Taylor, Robert; Committee Member: Weyand, Corneli

Role of noncoding RNA in vascular remodelling

Purpose of review: Noncoding RNAs (ncRNAs), such as microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) are becoming fundamentally important in the pathophysiology relating to injury-induced vascular remodelling. We highlight recent studies that demonstrate the involvement of ncRNAs in vein graft disease, in in-stent restenosis and in pulmonary arterial hypertension, with a particular focus on endothelial cell and vascular smooth muscle cell function. We also briefly discuss the emerging role of exosomal-derived ncRNAs and how this mechanism impacts on vascular function. Recent findings: ncRNAs have been described as novel regulators in the pathophysiology of vascular injury, inflammation, and vessel wall remodelling. In particular, several studies have demonstrated that manipulation of miRNAs can reduce the burden of pathological vascular remodelling. Such studies have also shown that exosomal miRNA-mediated, cell-to-cell communication between endothelial cells and vascular smooth muscle cells is critical in the disease process. In addition to miRNAs, lncRNAs are emerging as regulators of vascular function in health and disease. Although lncRNAs are complex in both their sheer numbers and mechanisms of action, identifying their contribution to vascular disease is essential. Summary: Given the important roles of ncRNAs in vascular injury and remodelling together will their capacity for cell-to-cell communication, manipulating ncRNA might provide novel therapeutic interventions

Diabetes mellitus and ischemic heart disease. the role of ion channels

Diabetes mellitus is one the strongest risk factors for cardiovascular disease and, in particular, for ischemic heart disease (IHD). The pathophysiology of myocardial ischemia in diabetic patients is complex and not fully understood: some diabetic patients have mainly coronary stenosis obstructing blood flow to the myocardium; others present with coronary microvascular disease with an absence of plaques in the epicardial vessels. Ion channels acting in the cross-talk between the myocardial energy state and coronary blood flow may play a role in the pathophysiology of IHD in diabetic patients. In particular, some genetic variants for ATP-dependent potassium channels seem to be involved in the determinism of IH

The living aortic valve: From molecules to function.

The aortic valve lies in a unique hemodynamic environment, one characterized by a range of stresses (shear stress, bending forces, loading forces and strain) that vary in intensity and direction throughout the cardiac cycle. Yet, despite its changing environment, the aortic valve opens and closes over 100,000 times a day and, in the majority of human beings, will function normally over a lifespan of 70-90 years. Until relatively recently heart valves were considered passive structures that play no active role in the functioning of a valve, or in the maintenance of its integrity and durability. However, through clinical experience and basic research the aortic valve can now be characterized as a living, dynamic organ with the capacity to adapt to its complex mechanical and biomechanical environment through active and passive communication between its constituent parts. The clinical relevance of a living valve substitute in patients requiring aortic valve replacement has been confirmed. This highlights the importance of using tissue engineering to develop heart valve substitutes containing living cells which have the ability to assume the complex functioning of the native valve

Shear Stress Induced mTOR Signaling in Cultured A7r5 Aortic Smooth Muscle Cell Line

Vascular intervention procedures such as balloon angioplasty and stent implantation lead to denudation of endothelium exposing the underlying smooth muscle layer to effects of blood shear stress. The effect of shear stress on smooth muscle cell signaling has not been studied in depth. In this study, we examined time dependent changes in activation of Akt, mTOR and p70S6k related signaling in response to orbital shear stress on cultured A7r5 cells. A7r5 cells cultured to subconfluence on 150mm culture dishes were subjected to orbital shear of 9.8dynes/cm 2 for zero, 5 min, 15 min, 30 min, 1h, 4h and 24h. The cells were found to be reoriented with shear. Immunoblotting demonstrated increased phosphorylation of mTOR/p70s6krelated signaling proteins, suggesting an association between mTOR/p70s6k related signaling and shear induced reorientation of vascular smooth muscle cells. These data may provide insight into possible pharmacological interventions to prevent or retard the development of restenosis

Biophysical regulation of stem cell behavior within the niche.

Stem cells reside within most tissues throughout the lifetimes of mammalian organisms. To maintain their capacities for division and differentiation and thereby build, maintain, and regenerate organ structure and function, these cells require extensive and precise regulation, and a critical facet of this control is the local environment or niche surrounding the cell. It is well known that soluble biochemical signals play important roles within such niches, and a number of biophysical aspects of the microenvironment, including mechanical cues and spatiotemporally varying biochemical signals, have also been increasingly recognized to contribute to the repertoire of stimuli that regulate various stem cells in various tissues of both vertebrates and invertebrates. For example, biochemical factors immobilized to the extracellular matrix or the surface of neighboring cells can be spatially organized in their placement. Furthermore, the extracellular matrix provides mechanical support and regulatory information, such as its elastic modulus and interfacial topography, which modulate key aspects of stem cell behavior. Numerous examples of each of these modes of regulation indicate that biophysical aspects of the niche must be appreciated and studied in conjunction with its biochemical properties

CD40 ligand inhibits endothelial cell migration by increasing production of endothelial reactive oxygen species

Background— The CD40/CD40 ligand system is involved in atherogenesis. Activated T lymphocytes and platelets, which express high amounts of CD40 ligand (CD40L) on their surface, contribute significantly to plaque instability with ensuing thrombus formation, leading to acute coronary syndromes. Because reendothelialization may play a pivotal role for plaque stabilization, we investigated a potential role of CD40L on endothelial cell (EC) migration